An example of a prior art DC power supply apparatus with an inverter is disclosed in, for example, Japanese Patent Application Publication No. 2001-190060 A published on Jul. 10, 2001. The power supply apparatus disclosed in this Japanese publication includes a rectifying circuit for rectifying an AC voltage, and a smoothing circuit for smoothing an output voltage of the rectifying circuit into a DC voltage. This DC voltage is, then, switched in an inverter having a switching device which alternates between a conduction state and a nonconduction state. A snubber circuit is used in association with the switching device. The snubber circuit includes a series combination of a diode and a capacitor, and a resistor connected in parallel with the capacitor. When the switching device changes from the conduction state to the nonconduction state, the capacitor of the snubber circuit is charged through the diode, and, when the switching device changes from the nonconduction state to the conduction state, the charge on the capacitor is discharged through the resistor.
Since the voltage increase across the switching device is suppressed by charging of the capacitor when the switching device changes from the conduction state to the nonconduction state, switching loss in the switching device can be reduced. On the other hand, when the switching device changes from the nonconduction state to the conduction state, charge on the capacitor flowing through the resistor is wasted in the form of heat. This decreases efficiency of the circuit and necessitates the use of a larger resistor to reduce generation of heat. This, in turn, causes increase in size of the DC power supply apparatus.
Therefore, an object of the present invention is to provide a DC power supply apparatus with an improved efficiency and with a reduced size.